A template typically comprises a plastic sheet with circular and/or elliptical openings of various sizes and shapes formed therein to permit a draftman to reproduce the ellipses, circles or other shapes by placing the template over the work with respect to which he is engaged and tracing the shape of the opening on the work. Frequently, it is desired or necessary to be able to produce concentric circles, ellipses or other traced shapes with respect to a given template shape, conforming to the template design yet of different dimension. These remarks apply to template form defined cuttings as well as markings or tracings.
The prior art has produced a multiplicity of such devices, as will be evidenced by some of the citations given herebelow. However, the prior art devices suffer from a number of shortcomings. For example, many of the devices are excessively expensive to produce in operative form, either because of cost or because of the complexity or delicacy of the parts of the device. Other devices are not adaptable to varying circumstances, shapes or template forms; that is, they are not sufficiently versatile in use. Other devices fail to retain accuracy as they trace within or around the template configuration. Still other devices are limited to work in a specific or special environment and are not generally adapted to engineering template work.
What is desired is an extremely simple device which may be employed with template forms, both external and internal, of the most varied shape. Still another desired feature would involve the device being produceable in a multiplicity of sizes (to form a complete set for a given drafting purpose), all of the members of the set having a congruent pattern of form, differing only in size and placement of the operative parts thereof to achieve the various goals. Yet further, the device must be rugged, simple, have all the portions thereof readily available for cleaning and be relatively cheap to manufacture in mass production, while retaining exact construction and configuration for use in precise drafting work.